Fire authorities said a gas leak or a stove could have caused Thursday's blaze in the capital, which spread quickly after breaking out in a biryani restaurant, and was only reined in following two hours of effort by 13 units of firefighters.

A massive fire in Bangladesh that raged through a six-storey building home to restaurants where many families with children were dining has killed at least 46 people and injured dozens, the health minister said on Friday.

Fire authorities said a gas leak or a stove could have caused Thursday's blaze in the capital, which spread quickly after breaking out in a biryani restaurant, and was only reined in following two hours of effort by 13 units of firefighters.

Hospitals are treating 22 people with burn wounds, Health Minister Samanta Lal Sen told reporters.

"All 22 people ... are in critical condition," Sen, himself a well-known physician, said after a visit to the Dhaka Medical College Hospital. "We are trying our best to save their lives."

Prime Minister Sheikh Hasina expressed shock and sorrow at the incident, ordering swift treatment for the injured.

One survivor, Mohammad Altaf, recounted his narrow escape from the blaze that killed two colleagues.

"I went to the kitchen, broke a window and jumped to save myself," he told reporters, adding that a cashier and server who urged people to leave during the first moments had died later.

Firefighters used cranes to rescue people from the charred building, said fire officials, who were still working to clear debris and douse any remaining embers.

Relatives gathered at the hospital early on Friday to receive the bodies of the dead, with some mourning outside the emergency department.

Doctors said most of the dead were killed by suffocation with others dying as they jumped off the building, which also houses some clothing and mobile telephone shops.

Smoke billowed from the side of the building in video images filmed by a witness on Thursday.

The fire could have originated from a gas leak or stove, said Brigadier General Main Uddin, a top fire service official.